Well, having dealt with a few such cranks of late, I would not recommend ta pping the holes at 100 BCD unless the crank is in fact a Campy NR double wh ich you are trying to convert to as close to an original Campy NR triple as possible. Campy NR is the only such crank I know of that uses the 100 B CD circle, and I've never seen a Campy 100 BCD ring in anything but 36T, ev en though the circle should allow 32T, maybe even 30T. I believe (Jim?) Merz did make some rings as small as 32T to fit the Campy NR triple, but go od luck finding one of those, so unless one of the modern Campy triples use s 100 BCD for the inner ring, you will be limited to 36T, which is much lar ger than that circle should allow.
Avocet/Ofmega triples actually have two sets of inner drillings. The lar ger is 102 BCD, which is unfortunate, since if Ofmega and Campy had used th e same circle, at least those two brands could have interchanged. Kind o f like Zeus and Stronglight doubles being only 2 mm apart at 120 and 122mm. Avocet/Ofmega 102 rings are available in several sizes, the smallest be ing 32T I believe, but they are becoming somewhat rare. A much better ch oice might be the smaller Avocet inner circle of 74 BCD. There are a lot more Avocet/Ofmega rings around in that circle, plus many more recent, tho ugh not necessarily current, cranks used 110/74 circles, so there should be lots of 74 mm rings around.
I've been messing with a Stronglight 107 triple of late. Models 106 and 107 had gone to a 144 double circle, but the 107 (and perhaps 106) triple w as drilled at 86 BCD. That made sense, since that was the Stronglight mo d 99 circle. There were a lot of Mod 99's made, and they used the 86 mm circle for all rings and were frequently configured as triples, so mod 99 r ings in sizes suitable for an inner triple are still pretty easy to find.
The other triple with the inner holes tapped into the spider arms I'm a lit tle familiar with is the TA Tevano, or at least I'm familiar with the inner chainring bolts. I bought three sets hoping the would work for the Stro nglight 107 or Avocet, but they do not. Chris Kulczycki at Velo Orang e was until recently selling some Tevano arms that appeared to me to be dri lled for an inner ring, although I don't think he discussed that capability . Don't know what the cirlce is, but probably Chris does. It might be the Cyclotourist inner circle, although this would offer no advantage, as the Cyclotourist inner rings are 6 hole, while the Tevano is a 5 arm Campy clone.
So I think that other than to replicate a Campy NR triple by drilling NR double rings at the same BCD, you are best advised to use either a 74mm o r 86mm circle. But the other question is the hole size and thread. Af ter receiving the Tevano bolts, I found they are too small to fit Stronglig ht 107 or Avocet triple cranks. However Avocet bolts do work on Strong light 107, and it turns out both appear to use a standard M6 x 1 thread. The Tevano looks like 5mm, possibly a standard M5 x 0.8 thread. Anyone know what the Campy NR triple uses? If it is 5mm, maybe the Tevano bolts will work on the Campy arms. Last weekend I put together the Strongligh t 107 triple, using standard M6 x 1 bolts and chainring spacers. It look s like M6 x 1 stainless socket head or button head bolts either 16 or 20 mm long will work best, with chainring spacers somewhere between 7 and 11 mm. It looks like the spider arm thicknesses and profiles vary enough that different thickness spacers will be required for different brand arms, and Tevano and perhaps Campy will require M5 rather than M6 bolts. I'm not at all sure I have the right spacers to give the optimum spacing between mi ddle and inner ring, may have to actually install the crank on a bike to so rt that out. I'm also going to check my Campy triple to see what size th e holes are. Someone told me offlist that he bought some Avocet inner bo lts to use on a Campy and they didn't fit, so I assume Campy is something o ther than M6 x1.
It is no doubt a sign of age and weak legs that I have to begin researching triple chainrings.
Regards,
Jerry Moos
Big Spring,Texas, USA
From: bruce thomson <masi3v4me@yahoo.com> Subject: [CR]Seeking the "tripleizer" for tapping the Campy crank to a trip le To: Classicrendezvous@bikelist.org Date: Thursday, September 18, 2008, 1:22 PM
Listers: There was someone on the list who was offering to tap out stand ard drive arm to accept the inner 'granny' or triple chainrings on the Camp agnolo cranks. They offered the classic BCD of 100 for the original 36t ring or anothe r BCD to accept the more prevelant other ings.Does anyone know who it is or if that person would get hold of me either on or off list?
Bruce Thomson Spokane WA 99204 (509) 747 4314 Masi3v4me@yahoo.com rapidfire10ring@hotmail.com